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MC > Task 4 > Flashcards

Task 4 Flashcards

1
Q

What does an MEG meassure ?

A

magnetic field produced by electrical currents (dipoles

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2
Q

What is the meassurment system of an MEG ?

A

femto tesla 10-15T

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3
Q

What are the two assumptions of MEG ?

A
  1. Can only measure electrical activity (current) that is parallel to the surface (tnagetial / Sulci neurons)
  2. Electric fields produced by the brain are really weak
    - > room must be shielded with aluminum / mu metal
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4
Q

Whare are the sensors lcoated of an MEG ?

A

Helmet

-> Each sensor consit of 3 transformers and pick up coils

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5
Q

What is a Gradient coil ?

A

-> meassures in x / y direction

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6
Q

What is a Magnometer coil ?

A

-> meassures in z direction

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7
Q

How and where do the signals flow detected by the sensors ?

A

-> Flow via superconducting flux transformer
(increases SNR)
-> Where: Travel to SQUIDS those record magnetic field changes

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8
Q

Why is the MEG so large ?

A

Because the squids must be keept cold at 4 degrees

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9
Q

What is meant by the inverse problem ?

A

-> Calculating via a computer program the Source of The Magnetic Field based on a set of assumptions/observation

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10
Q

What are the assumptions of an inverse problem ?

A
  • > Assume that brain is approx. spherical and that active areas can be represented by single/multiple current dipoles
  • > Minimum norm estimates: Assumes to know the shape of the head, dipole orientation and distortion
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11
Q

What are Event related fields ?

A
  • > Simmilar to ERP

- The average of MEG traces

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12
Q

Summarize EEG

A
  • > Direct meassure of activation
  • > is not limited to any neurons
  • > high temporal resolution
  • > limited spatial resolution
  • > Cheap
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13
Q

SUmmarize MEG

A
  • > Direct meassure of activation
  • > is limited to tangential neurons
  • > high temporal resolution
  • > limited spatial resolution
  • > Expensive
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14
Q

Summarize fMRI

A 
-> Indirect measure of activation
Represents changes in blood-oxygen levels (image is 4-6s behind)
-> Bad temproal resolution 
-> High spatial resolution 
-> Expensive
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15
Q

Why would we still use EEG over MEG ?

A
  • > Less practical complaints /portable
  • > Sufficient spatial resolution
  • > Cheap
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16
Q

Why is MEG better then EEG ?

A

-> beacuse it has a higher spatial resolution beacsue the skull is more transparent for magentic fields !

17
Q

What are oscilaitions ?

A

-> The Brain waves which represent communication between spatially distributed bran networks

18
Q

What is Local-scale synchronisation

A

-> synchronisation – among neighbouring neurons

19
Q

What is Large-scale synchronisation

A

-> synchronisation – btw neuronal assemblies for distant brain regions

20
Q

How can you intepreted oscilations ? (high frequency)

A
  • > high frequency = originate from small neruons populations
  • > high frequency = low amplitude
  • > High degree of desyncronization
  • > high frequency = brain has something to do (state effect)
21
Q

How can you intepreted oscilations ? (Low frequency)

A
  • > low frequency = originate from large neruons populations
  • > Low frequency = High amplitude
  • > Low degree of desyncronization
  • > Low frequency = brain has nothing to do (state effect)
22
Q

Describe the Delta band:

A

1- 4 HZ

  • > Low frequency, high amplitude
  • > with Sleep + Highly present in the first two years of our life
  • > associated to proximity of brain tumors
23
Q

Describe the Theta band:

A

4 -8 HZ
-> Low frequency, high amplitude
-> Mostly sleep but:
o First: widespread scalp distribution -> drowsiness & impaired information processing
o Second: frontal-midline –distribution -> focussed attention, mental effort & effective stimulus processing

24
Q

Describe the Alpha band:

A

8-13 HZ

  • > Relaxed wakefulness and cognitive inactivity
  • > Lower alpha (8-10Hz) desynchronization -> stimulus unspecific expactancy
  • > Upper alpha (10-12Hz) desynchronization -> processing of sensory-semantic information, stimulus-specific expectancy
25
Q

Describe the Beta band:

A

13- 30 HZ
High frequency, small amplitude
Mostly present during cognitive activity -> focused attention or arousal

26
Q

Describe the Gamma band:

A

30 HZ and above
High frequency, small amplitude
Attention, arousal, object recognition, vigilance

27
Q

When is the P 3 component active ?

A
  • > Inreased when a given stimulus represents a category different from that of preceding stimuli
  • > “mechanism of assesing attitudes”
  • > stereotypes violation
28
Q

When is the N2 component active ?

A
  • > conditions invoking conflicting response possibilities

- > meachnism of effective priming

29
Q

when is the N 170 component active ?

A

face processing + Ingroup and outgroup favor

-> mechanism of perception

30
Q

When is the N4 active ?

A

violations of semantic processes/ sterotypes

31
Q

When is the ERN Error-related negativity active ?

A

higher amplitude in conflict monitoring processes

self regulation

32
Q

when is somthing active Below 200 ms ?

A
  • > Cognitive categorization

- > Both gender and race differntiation

33
Q

What is meant by frequency ?

A

Number of full cycles per second

1 Hz = 1

34
Q

What is meant by amplitude ?

A

Distance from zero to peak

meassured in microvolt

35
Q

What is meant by “phase” ?

A

shift of signal along the time axis

36
Q

what is meant by Frequency analysis ?

A

-> Oscillatory activity can be characterised by the sum of diff (single) waves with distinct frequencies & amplitudes and phase

37
Q

What is meant by the Frequency/Power spectrum ?

A
  • > Time on the x axis gets transformed to frequency

- > Y axis = amplitude stays the same

38
Q

What is meant by Fourier analysis ?

A

Decomposing a complex wave Irregular signal into its underlying single waves

39
Q

What is the difference between time frequency analysis and power sepctrum analysis?

A
  • > Power spectrum assumes a stationary process -> can not provide info about when in time frequency shifts
  • > Time frequency analysis can provide info about when in time frequency shifts!

MC (9 decks)

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